1. Field of the Invention
The present invention relates to a method for preventing optical disks from being scraped, and more particularly to a method for preventing optical disks from being scraped by a pickup head of an optical disc drive.
2. Description of the Prior Art
As the technology of digital multimedia has been rapidly improved over the last twenty years, it became fast and easy to handle a large number of data or information. For example, a great deal of data can be effectively and promptly written/read or stored/restored via optical recording media, such as an optical disk, through optical operating technology. The optical recording media has many advantages, such as small volume, portable property, easy restoration, and large data capacity, etc. Since the compact disk (CD) had been developed in the early time, many other types of CDs which have different functions have been developed in succession, for example CD-ROM, CD-RW, VCD and even the DVD (digital versatile disk) has a larger data capacity with better multimedia functions. An optical disc drive is a data read/write device which is integrated with optical, mechanical and electric operations, and through the operation of the pickup head of the optical disc drive, data can be read from or written in the optical disk.
FIG. 1 shows a basic structure and read/write operation of an optical disc drive. First, a beam of laser light is emitted from a laser diode 102 of a pickup head 100 in the optical disc drive. Following, the beam of laser light passes through a PBS 104, a collimator 106 and an object lens device 110 of the pickup head 100, then it focuses exactly on the concave 1182 of a data track of an optical disk 118 which is revolving at 200˜530 rev/min. The laser light is then interfered due to the coherency and optical property of the concave 1182 of the data track, and reflected by the read/write surface of the optical disk 118. Sequentially, the reflected laser light passes through the object lens device 110, the collimator 106 and the PBS 104 again and then it illuminates on a photodetector 116 through a cylindrical lens 114. Following, by a photo-electrical transforming mechanism of the photodetector 116, the optical signal which comes from the laser light is transformed into an electric signal (or electric current) to a micro processor (not shown) for detecting the information of the optical disk 118. The magnitude of the electric current from the photodetector 116 depends on whether the laser light from the object lens device 110 is focused on a concave, such as the concave 1182. The electric current will be smaller when the laser light is focused on a concave than when the laser light isn't focused on one. Accordingly, the information of the optical disk can be acquired via detecting variation of the magnitude of the electric current.
Accordingly aforementioned descriptions, the main operation of the pickup head 100 is using the focused laser light to scan the data track of the optical disk 118 and then sending the reflected laser light to a micro processor to detect the information of the optical disk 118 through the photodetector 116. Hence, its is necessary for the pickup head 100 to have precise focusing and tracking capabilities to get a good read/write performance. The focusing motion of the pickup head 100 is executed by controlling a voice coil motor 112 to drive the object lens device 110 upward or downward in a vertical direction to carry out the focusing servo operation; and the tracking motion is executed by way of controlling a sled motor (not shown) to drive the pickup head 100 along a horizontal surface parallel with the optical disk 118 to carry out the tracking servo operation, thus allowing the focal point of the focused laser light to exactly focus on the data track. Generally, when the pickup head 100 is conducting a read/write operation, the optical disc drive will take a focusing and tracking error signal to compensate the axial and radial wobble (or vibration) caused by the revolving optical disk 118 to make the focusing and tracking servo more precise.
The control gains of the focusing and tracking servo will be regulated in a self-adjusting process at the beginning when the optical disc drive is started. However, after the self-adjusting process is accomplished, the control gains will not be adjusted any more. Therefore, after the optical disc drive starts to conduct a read/write operation, if a exceptional reflection condition of the laser light has occurred; or there are opaque smears or dust on the read/write surface of the optical disk 118; and or the inner mechanism of the optical disc drive has experienced operation troubles, the optical signal (the laser light) reflected from the optical disk 118 will be faint and indistinct, thereby that makes the micro processor receive a faint electrical signal from the photodetector 116 and prevent a clear detection of the information of the optical disk 118 via the electric signal. At this time, the micro processor will consider the focusing servo has failed, i.e. the laser light didn't focus on the optical disk 118, and then it publishes a control signal to the pickup head 100 to move the object lens device 110 upward and downward to proceed focusing motion again.
However, no matter how the object lens device 110 moves, the photodetector 116 and micro processor can not receive a clear signal all the time, since the opaque smear or dust on the optical disk 118 or the operation troubles of the inner mechanism still exist. Hence, the optical disc drive loses its detecting basis for proceeding the focusing servo and the movement of the object lens device 110 can not stop, and then continues the focusing motion. At this time, the object lens device 110 may most probably scrap or damage the optical disk 118 in a upward focusing motion and crash the inner mechanism of the optical disc drive in a downward focusing motion, and that makes the optical disk 118 or the optical disc drive to malfunction, even more, it causes the inner circuit of the optical disc drive to burn out.
Due to the above-mentions, it needs to provide a method and apparatus for preventing the optical disk and the inner mechanism of the optical disc drive from being scraped and crashed by the object lens device of the pickup head during a read/write operation to increase the service life of the optical disk as well as the optical disc drive.